1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method for updating a location in a wireless communication system.
2. Discussion of the Related Art
A description will first be made of idle mode of a Mobile Station (MS) and a paging group.
A broadband wireless access system supports idle mode to minimize the power consumption of MSs. Generally, idle mode is intended as a mechanism to allow an MS to become periodically available for downlink broadcast traffic messaging without requiring the MS to register to any particular Base Station (BS) as the MS moves in a radio link environment populated by multiple BSs.
The idle-mode MS does not need to perform a handover process during moving between BSs within the same paging area. Therefore, the MS may save power that might otherwise be consumed to transmit uplink information for the handover procedure.
A paging area is defined as an area covered by a paging group including a plurality of BSs and paging is a function of, upon generation of an incoming call, locating an MS for which the incoming call is intended (e.g. detecting a BS or a Mobile Switching Center (MSC) to which the MS belongs). The paging group is a logical group. The purpose of the paging group is to offer a contiguous coverage area in which the MS can be paged on a downlink if there is traffic targeted at it.
A paging group may include one or more BSs and one BS may be a member of one or more paging groups. Paging groups are defined in a management system. A paging group may use a paging group-action backbone message. A paging controller may use another backbone message, paging-announce, to manage a list of idle-mode MSs and initiate paging of an MS on all BSs belonging to a paging group.
When an MS requests transition to idle mode to a BS, the BS may transition the MS to the idle mode by transmitting its paging group Identifier (ID) to the MS.
Conventional paging and location update procedures will be described below.
Upon receipt of an incoming call or a packet for an idle-mode MS, a paging controller transmits a paging message to all BSs within a paging group and, upon receipt of the paging message, each BS broadcasts a Paging Advertisement (PAG-ADV) message to MSs managed by the BS. The idle-mode MS checks the PAG-ADV message and if the paging controller has paged the idle-mode MS, it may enter normal mode and communicate with its serving BS.
If a location update triggering condition is satisfied, the idle-mode MS updates its location. There are timer-based location update, paging group location update, power down update, and Medium Access Control (MAC) hash skip threshold update.
If the MS moves out of the area of its paging group to the area of another paging group, the MS performs a paging group location update.
When the MS moves to the area of another paging group, it transmits a Ranging Request (RNG-REQ) message to a target BS to update its location. The target BS replies to the MS with a Ranging Response (RNG-RSP) message including a paging group ID, PG_ID. Then the target BS notifies the paging controller of the new location of the MS.
If the paging group is too small, the MS should perform a location update often. On the other hand, if the paging group is too large, a paging load is great.